Multiple bonding configurations of adsorbed formate on Ag{111}

The adsorption and reaction of the surface formate species on Ag{111} have been studied using a combination of reflection absorption infrared spectroscopy and temperature programmed desorption. Four formate species with distinct bonding configurations have been identified when formic acid is deprotonated by preoxidized Ag{111} at 240 K. Bidentate bridging formate with 2-fold symmetry is present at low coverage, while monodentate formate with three different degrees of tilt are formed sequentially with increasing coverage as a result of dipolar interactions and steric crowding. Coadsorption of methoxy and formate, accomplished by nucleophilic displacement of methyl formate with surface atomic O, yields an intermixed surface phase where interadsorbate interactions are minimized and formate tilting is suppressed. Monodentate formate partially decomposes to CO2 and formic acid at 325 K and partially reverts to bidentate bridging formate which dehydrogenates at 350 K to give CO2 and H2. © 1996 American Chemical Society.